1. Field of the Invention
The subject invention relates to twist beams for automotive vehicles, and more particularly to tubular twist beams, and methods of forming tubular twist beams.
2. Related Art
Automotive vehicles include torsion beams to connect the two rear wheels together through the use of longitudinal control arms. A particular type of torsion beam used on rear suspensions is a twist beam. Twist beams oftentimes comprise a tubular part having an O-shaped, C-shaped, U-shaped, or V-shaped cross-section, which is rigid enough to prevent bending and flexible enough to allow torsion. Accordingly, the tubular twist beam is not only a structural member, but also acts as a torsion spring. An example of a tubular twist beam is disclosed in U.S. Patent Application Publication No. 2010/0301577.
The weight of the tubular twist beam is preferably low because it contributes to the total weight of the automotive vehicle. However, tubular twist beams experience a significant amount of stress due to twisting and other factors. Therefore, maximum stress levels, especially those due to twisting, require a minimum material thickness and thus dictate the weight of the tubular twist beam.
The tubular twist beam is also used to control a roll rate of the vehicle, which affects the ride and handling of the vehicle. The roll rate is analogous to a vehicle's ride rate, but for actions that include lateral accelerations, causing a vehicle's sprung mass to roll. Roll rate is expressed as torque per degree of roll of the vehicle sprung mass, and is typically measured in Nm/degree. The roll rate of a vehicle does not change the total amount of weight transfer on the vehicle, but shifts the speed at which and percentage of weight transferred on a particular axle to another axle through the vehicle chassis. Generally, the higher the roll rate on an axle of a vehicle, the faster and higher percentage the weight transfer on that axle. A slower weight transfer reduces the likelihood of vehicle rollover conditions. The dimensions and design of the tubular twist beam have a significant influence on the roll rate of the vehicle.